lighter-than-air vehicles - Defense Innovation Marketplace

APPENDICESAppendix A- BalloonsIntroductionBalloons are not considered within the scope of this report; however, they will be addressed herebriefly as they utilize similar technology and often provide precursor experimentation in thedevelopment of other LTA vehicles. The AFRL maintains the only active balloon programwithin the DoD. There have been recent attempts to employ balloons with payload returnvehicles to operate similarly to high-altitude airships, but these efforts are no longer fundedwithin the DoD.Technology OverviewBalloons are typically defined as free-floating envelopes capable of carrying payloads to highaltitudes. They range in size from small weather balloons that may be launched by hand to verylarge balloons capable of carrying payloads of up to 8,000 lbs. Free floating envelopes can carrypayloads to stratospheric altitudes (up to 150,000 ft. MSL) or higher. 55 Without propulsion theballoon’s direction and speed are subject to the atmosphere’s prevailing winds, and balloons areunable to maintain position over a given area. A technique of releasing multiple balloons atstrategic intervals is often employed for applications such as remote communications relays thatrequire persistence over an area. 55A much less common type of balloon is a steerable balloon, which includes a mechanism forstation-keeping to enable persistence. 56 The propulsion is typically provided by the addition of apayload return vehicle (PRV), which allows the balloon to operate similarly to a conventionalairship. 57,58 These LTA vehicles differ from conventional airships in that the balloon (envelopesection) is considered disposable and is discarded at the end of each flight. The payload isintegrated into a PRV that detaches from the envelope near the end of the flight and is guidedback to a dedicated retrieval sight. The PRV is operated as a UAS glider on its return flight.Balloons capable of operating in near space (upper stratosphere) come in two types: zeropressureand super-pressure. 56 Both types typically use helium gas for lift and are made of avariety of common plastic materials such as latex or polyethylene. 59 The zero-pressure balloons,such as weather and recreational balloons, have openings so the pressure remains the same insideand outside the balloon; thus as the balloon rises, the volume expands to maintain a zero-pressuredifferential. These balloons will rise until they burst, find a buoyancy point, or lose lift via gasdiffusion through the permeable material. If a polyethylene balloon achieves neutral buoyancy, itcan stay up for a month or more. 56 The super-pressure balloons are completely sealed andmaintain higher pressure inside the balloon in order to maintain altitude during night and daytemperature changes. The balloons are typically launched partially filled with helium and as theballoon rises the helium expands to fill the balloon as it reaches the desired float altitude. 59Scientific BalloonsThe USAF operates the only active DoD balloon research program from Kirtland Air Force Base(AFB) in New Mexico. The Air Force’s High-Altitude Balloon Program is conducted by theAFRL Space Vehicles Directorate, Integrated Experiments and Evaluation Division. TheA-1